Thanks for all. Exquisite information.
I used fake ground on the bunker cause I suspected there was no option to dig, but anyway I wanted to be sure.
Note: Right now I'm working on objects for "the atlantik wall". The first battery is like those in Longues-sur-mer, the same as the bunker type M272. The last picture will become a 38cm Gun like those in Hanstholm II, covering the path between denmark and norway (still can be seen its remains with google maps. Allies never tried that path).